1. Field of the Invention
The present invention relates to Universal Serial Bus USB device, and more particularly to a USB device having a logical circuit for reset, that is, connection/disconnection to/from a USB host.
2. Description of the Related Art
FIG. 1 is a block diagram showing the relation between a Universal Serial Bus (USB) device and a USB host. Referring to FIG. 1, a system 10 equipped with a USB device 114 and a personal computer (PC) 20 equipped with a USB host 210 are connected via a USB cable 220. The USB device 114 is connected to the USB host 210 included in the PC 20 through a transceiver 116 and the USB cable 220.
In the configuration of FIG. 1, if a reset of the system 10 is initiated, an Application Specific Integrated Circuit (ASIC) chip 110 and a Central Processing Unit (CPU) 112 perform the reset operation. However, the PC 20 cannot recognize the reset of the system 10 connected via the USB cable 210. As a result, even though the reset of the system 10 is initiated in order to change the configuration of the USB device 114, the USB host 210 and the PC 20 cannot recognize the reset, and continuously maintain the unchanged configuration information of the USB device 114.
The PC 20 does not request configuration information of the USB device 114 until a user disconnects the USB cable 220 from the PC 20 and the system 10 and connects the cable again. Whenever the system 10 needs to be reset in order to change the configuration information of the USB device 114, the user must disconnect and reconnect the USB cable 220.
In addition, the reset is necessary when the USB device 114 malfunctions or an error happens in the system 10. In that case, the user must also disconnect and reconnect the USB cable 220. That is, the USB cable 220 is pulled out from a plug 120 and then inserted into the same plug 220. When the USB cable 220 is inserted into the plug 120 again, the PC 20 performs a hot plug & play, recognizes the USB device 114 and receives the configuration information from the USB device 114. Here, the term “hot plug & play” means that the PC 20 recognizes the USB device 114 immediately after the cable is plugged in.
As described above, in order to reset the existing USB device 114, the user, in an inconvenient manner, has to unplug and plug the USB cable. As one solution to the problem, existing conventional art emulates a plug-out and plug-in of the USB cable, allowing the user to reset the USB device by pressing a switch in the USB system or in the USB device. However, the conventional art does not offer the best solution in the true sense in that it requires user's intervention.
Therefore, the existing USB reset methods, in addition to creating inconvenience to the user, do not allow for easy control of the reset operation time.